1. Field of the Invention
The present invention relates to a vibration isolator for preventing the transmission of the vibration from a member which generates vibration, and portionicularly to a vibration isolator which can be adopted for a fluid-filled type vibration isolator which is applicable to engine mounts, bushings, and the like for motor vehicles.
2. Description of the Related Art
For example, between the engine, which provides the vibration generation portion of a vehicle, and the vehicle body, which provides the vibration reception portion, a vibration isolator as an engine mount is disposed to absorb the vibration generated by the engine thereby preventing the vibration from being transmitted to the vehicle body.
And, as an example of this type of vibration isolator, a vibration isolator as a controlling mount has conventionally been known which is filled with a fluid and has a structure capable of changing over the orifice, i.e., the passage for the fluid, in order to accommodate the vibration having a wide range of frequency.
In other words, for such a vibration isolator, not only an electric actuator, a solenoid valve, or the like, for changing over the passage among a plurality of orifices has been required, but also a controller for operating the actuator, solenoid valve, or the like, on the basis of the traveling conditions for the vehicle, and changing over the orifice has been required from the nature of the structure.
However, such an actuator, solenoid valve, and controller are relatively costly, and thus these components have been a factor for increasing the cost for manufacturing the vibration isolator.